NBS BUILDING SCIENCE SERIES 81

U.S. DEPARTMENT. OF COMMERCE / National Bureau of Standards

Survey of Ground Fault Circuit

Interrupter Usage for Protection

Against Hazardous Shock
NATIONAL BUREAU OF STANDARDS

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or BTANDAfiDa

JUL 2 7 1976

Survey of Ground Fault Circuit Interrupter

''fA^'^

Usage for Protection Against Hazardous Shocks

OCd lSciAlo('<ns Sc/e/ice- S'e.n'c-s' mo,^(

k « k y

Robert W. Beausoliel

and

William J. Meese

Building Environment Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assisfanf Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acfing Director

Issued March 1976
Library of Congress Cataloging in Publication data

Beausoliel, Robert W.

Survey of ground fault circuit interrupter usage for protection

against hazardous shock.

(National Bureau of Standards building science series ; 81)

Bibliography: p. Supt.ofDocs.no.: c 13.29/2:81.

1. Electric circuit-breakers. 2. Electric shock. 3. Building

Electric equipment—Safety measures. I. Meese, William J., joint author. II. Title. III. Series: United States. National Bureau of Standards. Building science series ; 81. TA435.U58 no. 81 [TK2842] 690 .021 s [621 .317] 76-608069

National Bureau of Standards Building Science Series 81

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 81, 19 page^. (Mar. 1976) CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1976

For sale by ihe Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.29/2:81) . Price 45 cents. (Add 25 percent additional for other than U.S. mailing).
Preface

Information in this report concerning ground fault circuit interrupters (GFCIs) was obtained primarily from a literature search by Miss Maggie Cason of the NBS library. The library has access to a number of computerized bibliographic retrieval services. The services were obtained through the use of

a terminal and telephone communication link at NBS, using the retrieval systems of vendors. Also, to closely span current GFCI usage in the United States, it was necessary to search for that time not covered by the computer service. The basic search used the following data bases:

(a) Computer search of The National Technical Information Service, 1964 to present

(b) Manual Search of U.S. Government Research and Development Reports, 1960-1963.

(c) Computer search of INSPEC (Computerized Electrical and Electronics Index), 1969 to present.

(d) Manual search of Electrical and Electronic Engineering Index, 1960-1968.

(e) Computer search of Compendex (Computerized Engineering Index), 1970 to present.

(f) Manual search of the Engineering Index, 1960-1969.

iii

Contents

Page

1. Introduction 1 1.1. Flat conductor cable in buildings 1 1.2. Scope 1

2. Shock hazards to the human body 2

2.1. Line-to-ground shocks 2

2.2. Line-to-line shocks 2

2.3. Currents in the human body 2

2.3.1. Perception currents 3

2.3.2. Reaction currents 3

2.3.3. Let-go currents 3

2.3.4. Currents slightly above "Let-go" levels 3

2.3.5. Currents causing ventricular fibrillation 3

2.3.6. Effects at higher currents 4

2.4. Frequency aspects 4

3. Means to protect against shock hazards 4

3.1. Isolation 4

3.2. Isolation transformers 5

3.3. High frequency/direct current 5

3.4. Guarding 5

3.5. Insulating 5

3.6. Double insulation 5

3.7. Grounding 5

3.8. Shock limitation 6

4. Functional description of GFCIs 6

4.1. Functional characteristics 6

4.2. Test circuits ^

5. Protection against fire ^

6. History of GFCIs 7

7. GFCI regulatory provisions ^

7.1. National Electrical Code ^

7.2. Occupational Safety and Health Administration 8

7.3. Other authorities ^

8. Ground fault equipment in U.S.A ^

8.1. Groups of GFCIs 9

8.2. Classes of Group 1 GFCIs ^

9. Manufacturers and costs of GFCIs ^

10. Installation of GFCIs 9

10.1. U.L. installation requirements ^

10.2. Single sensors ^

10.3. Leakage current problems • ^

10.4. Inductive circuit problems

10.5. Loss of lighting problems

11. GFCI testing and research

11.1. U.L. tests 11.2. U.L. field investigations 10

11.3. GFCI performance tests

11.4. Routine tests

V
Page

12. Foreign experience 11

13. Controversies concerning the use of GFCIs 11

13.1. Arguments for the use of GFCIs 11

13.2. Arguments against the use of GFCIs 12

14. Summary 12

15. Recommendations 12

16. References 13

vi
Survey of Ground Fault Circuit Interrupter Usage for

Protection Against Hazardous Shock

Robert W. Beausoliel and William J. Meese

The ground fault circuit interrupter (GFCI) is increasingly becoming an integral part of building electrical systems to protect human life. Building researchers, designers, and contractors should have a working knowledge of their purpose and operational characteristics. This report describes the functional principles of GFCIs and relates their performance to effects of electric current on the human body. Information concerning the history, research and testing, installation practices, fire protection aspects, types, manufacturers and costs of CFCIs are included. The trend

of requiring installation of GFCIs on more and more electrical circuits by regulatory authorities for safety purposes is outlined. Controversies concerning feasibility, reliability, nuisance tripping and other problems are discussed; laboratory and field investigations addressing these problems

should be undertaken. Permanent installations of GFCIs are being made in new residential and other construction, but very few are being installed in older buildings. The rationale for this needs to be examined. Because of higher leakage currents probable in most older construction, GFCIs manufactured

under present standards may not be feasible in older buildings.

Key words: Branch circuit protection; electric shock; electrical safety; ground fault; leakage

current; prevention of electrocution.

1. Introduction

The ground fault circuit interrupter (GFCI) is a

device designed to open an electric circuit when a ground fault current exceeds a certain value. Underwriters' Laboratories Standard 943 [1]^ defines ground fault as "denotes an unintentional electrical path between a part operating normally at some potential to ground, and ground." The National Electrical Code (NEC) [2] defines ground fault circuit inter- rupter as "a device whose function is to interrupt the

electric circuit to the load when a fault current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply current." Section 4 of this report contains a description of the functional principles of GFCIs.

In the U.S.A. most GFCIs are designed to operate

when current to ground exceeds 5 milliamperes (mA)

.

GFCIs will not function to protect against line-to-line

faults. Fuses or circuit breakers are required for this purpose. However, on most branch circuits, fuses or

circuit breakers will not operate until currents exceed

15 or 20 amperes (A), which is far above safe cur- rents through the body.

The need for a comprehensive report concerning

ground fault circuit interrupters (GFCIs) became ap- parent during a preliminary investigation by the National Bureau of Standards on the evaluation of the

possible use of flat conductor cable (FCC) in buildings. This investigation of FCC is being done for the U.S. Department of Housing and Urban Development.

^ Figures in brackets indicate literature references at the end of this publication.

1.1. Flat Conductor Cable in Buildings

Development of flat conductor cable (FCC) has

been primarily for aerospace applications. In recent

years, however, as a part of its technology "spinoff"

program, the National Aeronautics and Space Administration (NASA) has proceeded with a program

to adapt FCC for use in electrical and communication

circuits in buildings [3]. The geometry of FCC is such that more area of its conducting path is exposed to potential contact by

people, either directly or via metal building components, than is the case with conventional cable with

round conductors. Surface mounting of FCC, which

may provide economies in building construction, in- creases the possibility of such contact. The primary

proposed means of protection against shock hazards

of Fee electrical circuits is with ground fault circuit interrupters (GFCIs) [3]. While other means of protection, such as covering with grounded metal sheets,

may be feasible, a study of GFCIs became apparent as a prerequisite to the evaluation of FCC.

1.2. Scope

This report describes and analyzes the use of GFCIs

in buildings. The performance required of GFCIs is related to the effect of electric shock on the human

body. Other means of protecting against electric shock

are discussed. Protection by GFCIs against some, but

not all, electrically caused fires is discussed. Information is included concerning the history, research and

testing, foreign experience, installation practices, manufacturers, types, and costs of GFCIs.

1
Up to the present time, only round electrical con- ductors have been used in building wiring except in a few minor prototype installations of FCC. This report on the survey of GFCI usage assumes the use of con- ventional electrical cables with round conductors unless otherwise stated.

2. Shock Hazards to the Human Body

Generally, except for certain industrial or other

special applications, buildings in the United States are equipped with nominal 120 and 240 V, 60 Hz, single

phase electrical branch circuits. Both 120 and 240 V

circuits have 120 V with respect to earth and building

grounds. Figure 1 . describes a typical residential elec- trical service. The potential for shock exists when a person makes

contact between conductors at different potentials or between a conductor and ground. Referring to Figure

1 this may occur when a person gets across:

(a) A black or red wire and a white (neutral) wire;

(b) A black or red wire and ground;

(c) A black and a red wire or;

(d) A white (neutral) wire and ground. (This last case is usually not hazardous because the difference

in potential between neutral wires and ground is usually small.)

2.1. Line-to-Ground Shocks

When a person completes a circuit between a voltage source and ground, a current may flow through the body. In most electrical circuits this current path

would be an abnormal path. In this case a GFCI on the

circuit could remove the voltage quickly, preventing

death or serious injury to the victim. See functional

description of GFCI, Section 4.

2.2. Line-to-Line Shocks

Protection against shock (current through the body)

primarily depends on the design of electrical systems

and equipment, including circuit outlets. Adequate

electrical insulation and enclosures should prevent

inadvertent contact with current carrying elements. However, proper caution must be observed as it is difficult to protect a person who contacts two con- ductors which are at different potentials and both of which are intended to carry current under normal cir- cumstances. In this case a GFCI would not operate.

2.3. Currents in the Human Body

The magnitude of the current that may flow through

the body is determined by the potential difference or

voltage of the circuit, body resistance and other

resistances in series with the body. A person's skin

provides much of the body resistance. The resistance

of human skin varies with individuals. When drv

it may be as much as 100000 to 300000 ohms/cm'^

but when the skin is wet, or broken by a cut, the resist- ance may be only one percent of this value [4].

A value of 500 ohms is commonly considered to be

the minimum resistance of the human body between

hands or between other major extremities of the body

such as hand and foot. A resistance of 500 ohms is frequently used in estimating shock currents during

2
industrial accidents [4]. A current of 240 mA wouH

flow between hand and foot assuming a 500 ohm

resistance and 120 V potential (see Figure 2). Usually,

in the case of electric shock involving nominal 120 V

circuits, the current in the body is much less than

240 mA. The effects of various levels of current on

the human body are described below.

PANEL BOARD

CIRCUIT BREAKER

OR FUSE

INTERRUPTER SOLENOID

DIFFERENTIAj TRANSFORMER

L_ ELECTRO. _J

CIRCUITRY

GROUNDING CONDUCTOR

Figure 2. Illustration of GFCI operation. GFCI detects a fault current (assumed to be 100 mA) and opens circuit. Fault current is passing through person who feels shock until circuit is opened. Note: Without a break in the ground path, current would pass through grounding conductor and GFCI would open the circuit. In this case a person would probably not feel a shock.

2.3.2. Reaction Currents

Currents equal to or slightly greater than perception

currents could produce an involuntary reaction re- sulting in an accident. Such a current is known as the reaction current.

2.3.3. Let-go Currents

Except for the startling effect and involuntary move- ment which may result in an accident, the smallest

electric shock of importance is the current which

causes a loss of voluntary control of the hand when

grasping an electrified object [5]. When the current

is increased there comes a time when the victim can- not let go of the conductor; the victim is said to "freeze" to the circuit. The maximum current a person

can endure and still release the conductor by using

muscles directly stimulated by the current is called

his "let-go" current [4]. The following observation

concerning let-go experiments conducted over a 25- year period are given by Dalziel [4]

:

1. An individual's let-go current is essentially constant if sufficient time is allowed for recovery between shocks.

2. An individual can endure, with no adverse ef- fects, repeated exposure to the reactions asso- ciated with currents of his let-go level.

3. The physiological reactions resulting in the in- ability of let-go are essentially the same over the limited frequency range 50 to 60 Hz.

The maximum uninterrupted reasonably safe let-go currents are 9 mA for normal men and 6 mA for normal women. It has not been possible to obtain

reliable values of let-go currents for children [4].

2.3.4. Currents at or Slightly Above "Let-go" Levels

Currents at or a little above those at which a person

can "let-go" of a circuit, but below currents causing

ventricular fibrillation (see Section 2.3.5) may contract chest muscles and stop breathing during the period of the shock [4], [6]. Normal breathing may

resume when the current is interrupted. However,

with prolonged current collapse, asphyxia, unconciousness, and even death may occur in a matter of minutes.

2.3.5. Currents Causing Ventricular Fibrillation

2.3.1. Perception Currents

Depending upon body resistance and applied volt- age, the shock victim is subjected to a particular current level. The level at which alternating current stimulates the nerves is indicated by a slight tingling sensation and is known as the perception current. The mean

perception current value for men is 1.1 mA at 60 HZ

and the mean value for women is 0.7 mA [4]. (RMS

values are used in this paper)

Larger currents may produce an effect on the heart

that is medically known as ventricular fibrillation. Dalziel states that "from a pratical point of view,

this term means stoppage of heart action and blood

circulation." The human heart rarely recovers spon- taneously from fibrillation [4].

Ventricular fibrillation experiments cannot be con- ducted on man. The only recourse is to experiment on

animals and extrapolate animal data to man [4]. Such

data has been obtained by Kouwenhoven and others

[7]. It is believed that ventricular fibrillation in

3
'-TRIP VALUE AT ZERO LOAD (OAZIEL) (4) TYPICAL GFCI

1 I

I I I I I I I I I

I 1 I

I I I I I I

I 1 I I MM

01 1 1.0 10

TIME T- SECONDS

Figure 3. Characteristic elements—GFCI performance.

normal adult workers is unlikely if shock intensity is less than mA, where T is in seconds, as given

by Dalziel. See electrocution threshold curve in Figure

3. The shorter the exposure time to a given current

the less the energy that is experienced by the victim

[6]. Figure 3 shows the threshold relationship be- tween currents and time which may result in electrocu- tion (ventricular fibrillation) at 120 V, 60 Hz. Note

that values indicating the "let-go" threshold current and the current when the body resistance is at the anticipated minimum of 500 ohms are shown in this

figure.

2.3.6. Efifecls at Higher Currents

Currents greater than those which result in ventricular fibrillation may cause cardiac arrest, respiratory

inhibition, irreversible damage to the nervous sys- tem, serious burns and unconsciousness. No numerical

data are available for currents which cause these

effects [4].

2.4. Frequency Aspects

Perception currents and let-go currents increase considerably as frequency is increased. Relatively little

is known concerning the effect of frequency on fibril- lation currents. However, studies show that the cur- rent required to produce fibrillation in dogs at 3000

Hz is 22-28 times that at 60 Hz [4].

3. Means to Protect Against Shock Hazards

Eight means are known for reducing the hazard of

electric shock [4]. These eight means are described

below.

3.1. Isolation

Nationally recognized codes define "isolated" and

"isolation by elevation" as follows:

"Isolated means that an object is not readily ac- cessible to persons unless special means for access are used." [2] [8].

"Isolation by Elevation means elevated sufficiently so that persons may safely walk underneath." [8].

Elevating electric circuits to isolate them is common

practice for overhead transmission and distribution

lines. Isolation of electric circuits in buildings is not common except in some industrial and other special

purpose buildings.

4
3.2. Isolation Transformers

Isolation transformers are used to protect against

shock hazards primarily in medical equipment. [4] In Europe, however, they have been used on bathroom

circuits [9]. Safety is achieved because the secondary

of the transformer serving the load is ungrounded and

is isolated from the primary windings which are connected to the building supply. This isolation should

prevent hazardous line-to-ground shocks.

3.3. High Frequency/Direct Current

With high frequency alternating current (see Section 2.4) or with direct current, it has been demonstrated that people or animals are less vulnerable

to electric shock [4]. High frequency/direct current have principally been used as a means to protect

against electric shock in applications in the medical

field.

3.4. Guarding

Nationally recognized codes define "guarded" as follows

:

"Guarded means covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers

or casings, barrier rails or screens, mats or platforms, to remove the liability of dangerous contact or approach by persons or objects to a point of danger. [2] [8].

"Note: Wires which are insulated, but not otherwise

protected, are not considered as guarded." [8].

Most interior wiring which is a permanent part of a building is guarded. The wiring to many portable

lamps and appliances is insulated but not guarded.

3.5. Insulating

Nationally recognized codes define "insulated" and

"insulating" as follows:

"Insulated means separated from other conducting

surfaces by a dielectric substance or air space permanently offering a high resistance to the passage

of current and to disruptive discharge through the substance or space.

"Note: When any object is said to be insulated, it is understood to be insulated in a suitable manner

for the conditions to which it is subjected. Otherwise, it is within the purpose of these rules uninsulated. Insulating covering of conductors is one means for making the conductors insultated." [8]

"Insulating (where applied to the covering of a conductor, or to clothing, guards, rods, and other

safety devices) means that a device, when interposed

between a person and current-carrying parts, protects the person making use of it against electric shock from the current-carrying parts with which

the device is intended to be used; the opposite of conducting." [8].

3.6. Double Insulation

Double insulation denotes a term which applies to a system of insulating electrical equipment which is superior to and less likely to fail in service than more

usual methods of insulating. The National Electrical Code (NEC), Article 250-^5 (c), does not require

grounding of some portable tools and appliances protected by a system of double insulation [2]. Although

double insulation has had a good record, it may not be safe under certain circumstances. Dalziel states that double insulated electric shavers have caused two

or three electrocutions. The accidents happened when

the victim dropped the shaver into a water-filled toilet bowl or wash basin and immediately reached for it without first disconnecting the plug [4].

3.7. Grounding

Nationally recognized codes define "grounded" and

"effectively grounded" as follows:

"Grounded means connected to earth or to some

extended conducting body which serves in place of

the earth." [2]

"^Effectively Grounded means permanently con- nected to earth through a ground connection or

connections of sufficiently low impedence and having

sufficient current-carrying capacity to prevent the building up of voltages which may result in undue

hazard to connected equipment or to persons." [8].

Grounding requirements in Codes apply to both

circuits ("system grounds") and to conducting

materials enclosing electric conductors or equipment

("equipment grounds"). The National Electrical Code

[2] states that the purposes of grounding are:

"Circuits are grounded to limit excessive voltages

from lightning, line surges or unintentional contact with higher voltage lines and to limit the voltage

to ground during normal operation.

"Conductive materials enclosing electric conductors

or equipment, or forming part of such equipment,

are grounded for the purpose of preventing a

voltage above ground on these materials.

"Circuits and enclosures are grounded to facilitate overcurrent device operation in case of insulation

failure or ground faults."

5
The National Electrical Code recommends grounding of nonelectrical equipment through the following

statement. "Where extensive metal in or on buildings

may become energized and is subject to personal contact, adequate bonding and grounding will provide

additional safety." The Code requires that both

electrical and exposed non-electrical metal parts of mobile homes which may become energized be effec- tively bonded and grounded to the grounding terminal

or enclosure of the distribution panelboard.

A position paper prepared by an Ad-hoc Task

Force on Grounding for the National Commission on

Product Safety pointed out both advantages and dis- advantages in the practice of grounding appliances

and electrical systems [10]. This paper encouraged

the installation of GFCIs on circuits supplying 15 and

20 A outlets. With properly adjusted and maintained

GFCIs, the safety of cord-connected appliance usage

does not generally depend on the grounding of the ac- cessible metal parts of the appliance [10].

Practically all residences in the United States that use electricity are properly grounded (in accordance

with applicable Codes) at the service entrance point..

While grounding in residences has many advantages, some disadvantages are briefly summarized below:

(1) By having electrical systems grounded, anyone

in contact with the ground and touching a live part

will receive a shock [10].

(2) Equipment grounding increases the area of

possible contact and locations at which persons can

establish electrical contact with the earth. This can

increase the chance of shock because of more probable

simultaneous contact with a grounded object when

there is accidental contact with an intended live part.

(3) If an untrained or inexperienced user repairs the supply cord of a grounded appliance, he may make

improper connections that can cause the exterior metal parts to be connected to the live conductor in- stead of the grounding conductor. In this case the casing of the appliance may have a potential of 120

volts to ground. The referenced report states that ex- perience has shown that this is a real problem in the usage of three-wire grounding cords and plugs [10].

Connecting the ground wire to the wrong terminal

in replacing or repairing a plug resulted in 21 electro- cutions among 88 investigated in Australia [11].

While most recently built homes are equipped with

grounding-type receptacles, only about 15 percent of American homes constructed prior to 1970 had power

receptacles built to accept the plug with a grounding

prong. Users may install an adapter which connects

the grounding prong to a screw on the receptacle plate

to update non-grounding type receptacles. Even when

the adapter is used, however, the screw, plate, and

receptacles themselves may not be grounded [11]. One

survey of hospitals showed 55 to 100 plugs had the grounding prong clipped off and the ground wire was

broken in 30 out of 45 adapter plugs inspected [11].

An Underwriters' Laboratories study found that only

13 percent of the power tools in use in the United

States were properly grounded. [11]

3.8. Shock Limitation

Ground fault circuit interrupters limit the duration

and energy of a shock. Section 4 describes the functional principles of these innovative devices.

4. Functional Description of GFCIs

The functional description of a typical GFCI is shown in Figure 2. As long as the current flowing in the black wire equals the current flowing in the white

wire, the voltage in the secondary winding of the dif- ferential transformer is zero. If current above the trip

value of the GFCI flows to ground, such as shown in Figure 2, the solid state electronic circuitry causes

the interrupter solenoid to disconnect the circuit. Energy to operate GFCIs is supplied by the building

branch circuits.

4.1. Functional Characteristics

The functional characteristics of Group 1, Class A,

GFCIs (see Section 8) are described in this report.

The principle difference between Class A and Class B

GFCIs is the higher trip value (20 mA) permitted for Class B. A Group 1, Class A GFCI has a trip value of 5 mA

or less. A GFCI does not limit the current to ground

to 5 mA or some other value, but opens the circuit whenever its trip value is exceeded.

The upper value of line-to-ground current that a

person will experience on ordinary 120 or 240 V

branch circuits is approximately 240 mA assuming

that his resistance is 500 ohms (See section 2.3).

A person would probably feel the shock of this current before the GFCI opened the circuit. However, a GFCI

is designed to trip fast enough ( about 25 milliseconds

or less at 240 mA ) to prevent electrocution. See plot of

a GFCI characteristics (trip time versus fault current)

in Figure 3. UL requires that a Class A GFCI be capable of

interrupting the electric circuit to the load when

the fault current to ground is within the range of 5

to 264 mA in accordance with the following relation- ship: [1]

'=(7)

where T is in seconds and / is the fault current to ground in milliamperes. Figure 3 shows a plot of this equation which can be compared with the curves showing the electrocution threshold for adults, the

let-go threshold and maximum expected body currents on ordinary branch circuits. Analysis of available

6
data (on animals and adult humans) by Underwriters'

Laboratories indicated that protection against electro- cution for man, including a 2-year old child should

be provided if all combinations of body current and

duration are below the plot of the above equation [12].

GFCIs will not function to protect the circuit against

line-to-line overloads. A fuse or circuit breaker is required for this purpose. On most branch circuits,

however, a fuse or circuit breaker will not open a cir- cuit until current exceeds 15 or 20 A, which, of course,

is far above maximum expected currents through the body.

4.2. Test Circuits

GFCIs are required by Underwriters' Laboratories

to have a means whereby they can be readily tested at any time to determine if they will function if there is a ground fault [1]. Figure 4 illustrates a supervisory

circuit or test circuit. This circuit produces a ground

fault with a current slightly above the GFCIs trip value

(approximately 6-7 mA for a 5 mA GFCI ) within

the GFCI when the test button is pressed.

laboratory without tripping ground faull < iiiuil inlerru|)lers [13 |. On the other hand, if overlicallrig from

su(;h cormeclions causes deterioration of insulation,

permitting a line conductor to contact a grounded

object, the GFCI will readily trip.

6. History of GFCIs

Devices that interrupt an electric circuit when the ground fault current exceeds a predetermined value (which is less than that required to operate the over- current devices, e.g. fuses, circuit breakers) have

been known for many years. Such devices have been

used to protect high-voltage power lines since the 1920s. They were set to operate at 10 to 20 percent

of the maximum operating current or trip value of

the circuit overcurrent devices [6]. For example a power circuit breaker having an overload trip value

of 200 A was set up to trip on ground faults of only 20

to 40 A, which was considered a great achievement of the day [6]

.

Some 10 years later the importance of protecting

against low-voltage "burndowns" in industrial equipSOLID STATE

CIRCUfTRY

BtACK WIRE

LINE NEUTRAL WIRE

DIffERENTlAL TRANSFORMER

Figure 4. A GFCI supervisory circuit.

5. Protection Against Fire

Ground fault circuit interrupters are principally

used for protection against shock hazards. However,

they can provide protection against some fire hazards.

Fires which might start where overheating is occurring

between a line conductor and ground or where there

is arcing between a line conductor and ground may be

prevented by the fast action of ground fault circuit interrupters.

GFCIs will not open a circuit when overheating is occurring along the current -path until a ground fault occurs. Glowing electrical connections have been

established and sustained for many hours in the

ment was recognized in Germany. Subsequently, Ger- many developed devices having a line-to-ground-trip value of about 500 mA to protect industrial equipment [6]. About 15 years ago, the French and the Austrians developed two-wire earth-leakage circuit breakers having a trip value of 25 to 30 mA [6]. In Europe a GFCI device is called an earth-leakage cir- cuit breaker. The French-Austrian innovation was

followed in the U.S.A. in 1962 by the development

of the transistorized GFCI. having a ground-current

trip value of 5 mA. This means that the circuit breaker

will trip with a 5- mA line-to-ground fault current. The

5 mA trip level is now required by the Underwriters'

Laboratories Inc., and by the Canadian Standard Association for most GFCI applications [6].

7
7. GFCI Regulatory Provisions

Required use of GFCIs by regulatory authorities is increasing. Generally, provisions, requiring the in- stallation of GFCIs are first incorporated in the National Electrical Code [2] before becoming part of

State, local or other regulations.

7.1. National Electrical Code

The trend toward increased use of GFCIs is illus- trated by comparing GFCI requirements in the last three editions (1968, 1971 and 1975) of the National

Electrical Code (NEC) [14, 15, 2]. The NEC is de- veloped under procedures of the National Fire Protection Association and the American National Standards Institute and is a voluntary standard as published. However, because of adoption, (sometimes

with revisions) by State and local authorities, the

installation of electrical equipment in buildings

throughout the U.S.A. is generally in accordance with

the NEC.

The 1968 edition of the NEC [14] was the first edi- tion to mention GFCIs. It recommended that attach- ment plug receptacles in the area adjacent to swimming pools be installed on a circuit protected by a ground fault circuit interrupter. The 1971 Edition

of the NEC [15] required that receptacles located between 10 and 15 feet from the inside wall of a swimming pool be protected by a GFCI. It prohibited outdoor receptacles closer than ten feet from

a pool. The 1971 edition permitted the use of GFCIs

as one means of protecting against fault conditions

involving underwater lighting fixtures which might

result in electrical shock hazards. Also, the 1971 NEC

edition required that all electrical equipment used with

storable swimming pools be supplied with circuits protected by GFCIs. The use of GFCIs in boatyards

and marinas on receptacles used to provide shore

power for boats was suggested.

Quite widespread use of GFCIs was required by the 1971 NEC on dates subsequent to the effective date

of the Code. In residential occupancies all 120V,

single phase, 15 and 20 A receptacle outlets installed outdoors on or after January 1, 1973 were required

to have approved GFCI protection for personnel. Such

protection could be provided on branch circuits or on feeders supplying applicable branch circuits. The

use of GFCIs was suggested for other circuits, in other locations and in other occupancies. All 15

and 20 ampere receptacle outlets on single phase cir- cuits for construction sites were required to have

GFCI protection for personnel on or after January 1, 1974. For residential occupancies, (including mobile

homes and mobile home parks) in addition to receptacle outlets on outdoor circuits, the 1975 NEC [2]

requires that 120 V, single phase, 15- and 20-A

receptacle outlets in bathrooms have GFCI protection

for personnel. For construction sites, GFCI protection

is required except when receptacle outlets on permanent wiring are used or when power is supplied by

5 kW or smaller portable generators meeting certain requirements.

Branch circuits supplying under-water lighting fix- tures in swimming pools which operate at more than

15 V are required by the 1975 NEC to have GFCI

protection. Also, GFCI protection is required on

branch circuits supplying fountain equipment operating at more than 15 V. In general, other 1975 NEC

requirements pertaining to swimming pool GFCI protection are similar to those in the 1971 NEC. However,

the 1971 NEC suggested use of GFCIs in boatyards

and marinas was eliminated from the 1975 Code.

"Leakage currents inherent in boats" was the apparent

reason for this reversal in the trend to recommend

and require greater use of GFCIs each time the NEC

is up-dated.

7.2. Occupational Safety and

Health Administration

The Occupational Safety and Health Adminstraton

(OSHA) of the US Department of Labor is responsible

for issuing and enforcing regulations concerning the

safety of workers in places of employment. On July 1, 1974 OSHA, pending reconsideration of the requirement, postponed enforcement of the National Electrical Code provision requiring GFCIs on all 15 and

20 ampere receptacle outlets on single phase circuits for construction sites [16].

7.3. Other Authorities

In building and construction many authorities

issue regulations, specifications or other require- ments. For example the Oak Ridge National Laboratory requires GFCIs on outdoor receptacles within

15 feet of the inside walls of reactor pools [17]. To

determine requirements pertaining to the use of GFCIs, the authority having jurisdiction should be

consulted.

8. Ground Fault Equipment in USA

The Underwriters' Laboratories recognize two types

of ground fault equipment.

(a) The first type is ground fault sensing and relaying equipment. This equipment is designed to open

conductors at predetermined values of ground-fault

current not exceeding 1200 A [18]. This equipment

has peripheral interest to the purposes of this report.

(b) The second type is a GFCI which functions

to open a nominal 120 V to ground branch circuit when there is a fault current to ground exceeding some predetermined value. This fault current is far

less than that necessary to trip a circuit breaker or "blow" a fuse.

8
8.1. Groups of GFCIs 10. Installation of GFCIs

UL recognizes two groups of GFCIs [19]

:

(a) Group I GFCIs are to be used only on circuits which have grounding conductors. There is some

disagreement with this requirement regarding "older"

installations which do not have equipment ground

provisions [20]. Group I GFCIs are covered by UL

Standard No. 943 [1].

(b) Group II GFCIs are to be used only on circuits that do not have grounding conductors. [19] They

are intended for use with isolation transformers. No

UL standard exists for Group II GFCIs. They are not used in residential and commercial buildings and have no other general use. Therefore, Group II GFCIs are not considered further in this report.

8.2. Oasses of Group I GFCIs

There are two classes of Group I GFCIs: [19]

(a) Group I, Class A GFCIs may be used with most

utilization equipment. However, swimming pool cir- cuits installed prior to local adoption of the 1965

edition of the National Electrical Code are likely to exhibit sufficient leakage current to cause a Class A

GFCI to trip. A Class A GFCI must trip when the current to ground exceeds 5 mA. The required maximum trip time depends on the fault current, as shown

in figure 2.

(b) Group I, Class B GFCIs are restricted for use with under-water swimming pool lighting fixtures,

provided also that the fixture is not marked to specify

the use of a Class A GFCI. Class B GFCIs must trip

when the current to ground exceeds 20 millamperes.

The primary purpose of the 20 mA rating is for practicable reasons, that is to allow for the greater

leakage current to ground inherent in underwater

lighting systems of some of the older swimming pools. Class B GFCIs have far less use than class A GFCIs.

Recent underwater lighting systems have improved

leakage cui'rent characteristics.

9. Manufacturers and Costs of GFCIs

Five manufacturers have produced GFCIs with UL

listings as of June 1974. [19]. The GFCIs produced

by these manufacturers must be in compliance with

UL Standard 943 [1].

The list price for duplex receptacle type GFCIs and

for single circuit breaker, plug-in type GFCIs for panelboard installation may be $40 to |50 or more; the

price to contractors is usually less. The cost of port- able cord-connected GFCIs is usually more than twice

the cost of permanently installed GFCIs.

GFCIs are installed in three configurations as

follows: [21]

(a) They may be located in the breaker panelboard

and may be an integral part of the circuit breaker.

(b) They may be located in cord-connected form

for portable and temporary operation.

(c) They may be located in standard duplex re- ceptacle form. There are two forms of this GFCI. A

feed through type protects itself and other receptacles

and devices connected to it on the load side. The

second type, a "dead-end" type, protects only itself and any connected load.

10.1. UL Installation Requirements

UL requires the following installation requirements

to "minimize" false tripping: [19]

A Class A device may not be connected: [1]

(a) To swimming-pool equipment installed prior

to adoption of the 1965 National Electrical Code.

[22]

(b) To longer lengths of load conductor than in- dictated in Table 32.1 of UL Standard 943. A Class B device may: [1]

(a) Only be used with underwater swimming pool

Lighting fixtures but not with such fixtures that are marked for use with a Class A GFCI.

(b) Not be connected to longer lengths of load con- ductor than indicated in Table 32.1 of UL Standard

943.

10.2. Single Sensors

Conductors (except equipment ground) for a cir- cuit should pass through a single sensor: these con- ductors cannot be "shared" by any other circuit. [20]

For example, sometimes the neutral conductors for more than one branch circuit are combined in a jimction box. This technique cannot be used where a GFCI

is involved because this connection results in parallel return neutral paths for each of the branch circuits,

involved, resulting in an imbalance in the GFCI sensor. [20]

10.3. Leakage Current Problems

In January 1969, the American National Standards

Institute published a standard for leakage current for appliances [23]. The standard limits leakage currents

for portable cord connected 120V appliances to 0.5 mA and to 0.75 mA for stationar\^ or fixed appliances.

Underwriters' Laboratories Standard 943 [1] defines "leakage current" as "denotes aU currents including

9
capacitively coupled currents which may be conveyed

between energized parts of a circuit and (1) ground

or (2) other parts."

Leakage current of appliances has been reduced

over the years. Some older appliances were manufactured with leakage current limits of 5 mA and some of

these may still be in use [6]. In such cases, if GFCIs

trip at about 5 mA, the sum of normal wiring leakage

and likely leakage of appliances may result in GFCIs

tripping even though an electrical fault per se does

not exist. Leakage currents in older houses and older build- ings present practical problems, which need investigation. See section 12, Foreign Experience. Older houses

may present more of a shock hazard than new buildings, but the present thrust is for building officials to ignore existing electrical installations. The National

Electrical Code [2] requirements are not retroactive. Enforcing authorities are not, to any noticeable extent, attempting to require GFCIs in existing buildings.

However, excessive leakage currents of permanent

branch circuit wiring when added to the leakage currents of appliances or other utilization equipment may

make the use of 5 mA GFCIs impractical.

10.4. Inductive Circuit Problems

False trippings have occurred where there were

high voltage spikes during the opening of inductive

circuits with relays, contactors and similar equip- ment. This problem is said to be solved by the addition of a capacitor of proper size to limit the voltage

to a level which a GFCI can withstand. It is stated

that these problems are solved on an individual basis

by variation in relay and other inductive device design

[20].

10.5. Loss of Lighting Problems

One authority suggests that GFCIs should be used

with circuits supplying only wall and floor receptacles rather than ceiling or wall-bracket illuminating fix- tures [6]. This would preclude the loss of lights when

GFCIs operate. The rationale for this is that the

electric shock hazard is associated to a greater degree

with portable appliances than with ceiling or wall- bracketed illuminating fixtures.

1 1 . GFCI Testing and Research

As is the case with many safety devices, GFCIs only

operate when something is wrong. To assume that a GFCI will operate when there is a fault to ground

but not give false operations is an important aspect

of its technology.

11.1. UL Tests

Group I GFCIs are subjected to extensive tests by

the Underwriters' Laboratories in accordance with

their standard No. 943 [1]. GFCIs which meet this standard are "listed" by UL. UL uses the term

"list" and not the term "approve" regarding products

they consider to be satisfactory. As a private organization UL does not have authority to approve products.

Enforcing authorities; usually State, local or Federal

governmental agencies, approve products installed in buildings. However, listing of electrical products by

UL often becomes tantamount to approval by en- forcing authorities.

Test and other evaluations of GFCIs by UL cover

the following: [1]

(a) Resistance to corrosion

(b) Rainproof enclosures

(c) Grounding

(d) Frame and enclosure

(e) Provision for wiring system

(f) Insulation

(g) Accessibility to energized parts

(h) Internal wiring

(i) Field wiring

(j) Power-supply cord

(k) Receptacles

(1) Spacing

(m) Operating mechanism

(n) Supervisory circuit (o) Leakage current

(p) High-resistance ground fault (q) Resistance to false tripping

(r) Regulation

(s) Normal temperature

(t) Dielectric withstand

(u) Overload and motor starting

(v) Low-resistance ground fault (w) Endurance

(x) Abnormal operation

(y) Extra-low-resistance ground fault

(z) Short circuit UL requires instructions for safe and effective use

of GFCIs. Some of these instructions must appear on GFCIs and be readily viewable when the GFCIs are

installed.

11.2. UL Field Investigations

UL investigated GFCIs by placing 100 units in various locations throughout the USA [24]. Two

manufacturers supplied 50 units each. The test duration was eighteen months. During this investigation there were 46 incidents of automatic circuit interruption which appeared to be due to ground faults. The

cause of the GFCI operation was determined for nearly all of these circuit interruptions. In addition

there were 26 incidents of tripping believed to be

associated with local electrical storm .activity and

ten other incidents which could not be associated with

any specific cause.

11.3. GFCI Performance Tests

To assure that GFCIs will prevent electrocution. Dr. Archer S. Gordon, of Statham Instruments, Inc., Oxnard, California, administered 2400 shocks to dogs

10
under anesthesia [6]. Experiments that may produce

ventricular fibrillation cannot be made on man, and

the only alternative is to experiment on animals and

try to relate the experimental data to man. See section

2.3.5. Commercial 5 mA GFCIs were used. Dogs were con- nected electrically from the "hot" wire of the 120V

laboratory circuit to ground. The dogs were given

800 shocks with a current pathway between right fore- paw and left hind paw. This was to stimulate the frequently experienced arm-to-leg pathway in many

human electrocutions. No incidence of ventricular

fibrillation was observed. Eight hundred additional

shocks were then given to the dogs after electrodes were placed on the right forepaw and left forepaw.

None of these 800 shocks produced ventricular fibril- lation. However, 36 fibrillations were produced during

the course of 800 shocks applied with electrodes placed on opposite sides of the chest. This result is alleged

to be not important from a safety viewpoint, since such a pathway is unlikely in human accidents. Moreover, since the minimum current for producing ventricular fibrillation in mammals is approximately

proportional to body weight, the authority states that

it is evident that the GFCI will protect human beings,

including the very young [6].

11.4. Routine Tests UL requires that the supervisory circuit (test button)

circuit of a cord-connected GFCI be operated before an appliance is plugged into any receptacle protected by

the GFCI. See section 4.2. UL also requires that the supervisory circuit of permanently connected GFCIs

be operated upon installation and at least as frequently

as monthly. UL requires that the user be informed

that in the event of improper function of a GFCI when

the supervisory circuit is operated, he is to correct the cause of the malfunction before further use of the

device. [1]

12. Foreign Experience

The GFCI had wide applications in other parts of the world such as Germany, France, Australia and

South Africa, prior to extensive use in the USA. [9]

The primary problem in foreign experience was strik- ing a proper balance between a trip value low enough

to provide protection but high enough to prevent

nuisance tripping because of leakage currents en- countered in wire, appliances and other electrical equipment. The sum of all leakage currents on the load side of a GFCI will be sensed by the GFCI.

In South Africa, units rated at 5 mA had to be

taken off the market due to nuisance tripping [9].

After a three-year investigation, the South African

Bureau of Standards agreed to 20 mA as a safe trip

value and satisfactory protection has been reported

with GFCIs rated at 20 mA. In France good experi- ence with 40,000 units with a 30 mA trip rating has

been reported. [9].

13. Controversies Concerning

the Use of GFCIs

In spite of research, testing and in-use experience,

there is considerable controversy over the merits of GFCIs. Comments stating why GFCIs should be re- quired in various locations, comments challenging

their need, their reliability, and problems they create are contained in (1) the pre-print of Proposed Amendments to the 1974 National Electrical Code (NEC)

[25] and (2) in public hearings held by the Occupational Safety and Health Administration in December,

1973 [26]. Some of these comments expressing various

points of view are listed below. (The 1975 edition of the NEC [2] was originally scheduled to be the 1974

edition)

.

13.1. Arguments for the Use of GFCIs

". . . With the greatly increased use of electrical appliances in the home, especially in the kitchen,

bathroom and garage areas, danger of personal injury

through ground fault conditions have also increased. There is now more contact with various types of

electrical equipment than ever before. Requirements

of ground fault protection on potentially dangerous

outlets can save hundreds of lives annually. Since the NEC has almost sole responsibility in safeguarding

the consumer in this area, . . ." [25]

". . . The shock hazard associated with out-door

receptacles exists regardless of location. More than

half of the electrical accidents occur in other than

residential occupancies. Many cord-connected appli- ances used in the home, hotels, motels and similar

dwelling occupancies are of the two-conductor non- grounded type. These appliances become particularly

hazardous when the user is grounded or exposed fre- quently to ground." [25]

". . . Hand-held appliances used in kitchens are normally not provided with a grounding conductor,

and the user is exposed to possible shock hazard from

the use of these appliances in association with water and grounded surfaces." [25]

". . . The bathroom is one of the most hazardous

places in residential occupancies for people using

electrical equipment, and since a receptacle is now

required in bathrooms, protection equal to the protection required for personnel using out-door receptacles should be provided in bathrooms also." [25]

". . . The Corps of Engineers states, * * * this survey shows that 294 contractors performing various types

of construction work are using ground-fault circuit protection. All units were reported to be operating

to the satisfaction of the contractors' . . ." [26]

"... A total of 52 fatal accidents which could have

been prevented by the use of GFCIs on construction

sites was found by studying all the data submitted.

11
This data covered the period from January 1970 to September 1974 . . ." [26]

13.2. Arguments Against the Use of GFCIs

". . . The Electrical Employers Self-Insurance Plan

of New York City, which maintains accurate accident

statistics for approximately 22 million manhours of construction work per year reports that they have

had no accidents that would have been prevented by

the use of the ground fault interrupter . . ." [25]

". . . The devices are still subject to unexplained trip- outs which result in shut-downs of production usually

for more than one craft and probably eventual by-pass

of the device." [25]

". . . It is my recollection that the Panel agreed that GFCIs are not practical on shore power receptacles

because of leakage current inherent in boats . . ." [25]

". . . The present ground fault interrupters for per- sonnel protection have sensitivity trip level of 5 mA.

Due to the fact that some portable dishwashers and

frost-free refrigerators contain calrod heating units which have leakage up to 100 rnA when energized, it would be impractical to require ground fault interrupters where these are used. Additional research in the form of fact finding studies must be accomplished

before requirements of this magnitude are made

mandatory." [25]

". . . It is felt that further approval of ground-fault

circuit protection should be withheld pending the establishment of some solid favorable evidence on the performance of ground-fault circuit protection presently being required for outdoor residential outlets under this section. It is noted that several of the Western European countries, with several years experience, have established a 20 mA trip position as being

appropriate while our requirements are only 5 mA"

[25].

". . . Some commenters expressed concern that many

GFCIs tripped well under 5 mA (i.e., 2.5 mA or less)

. . ." [26].

". . . Many commenters claimed that this standard

would have a severe economic impact. Some commenters claimed it would cost hundreds of thousands

of dollars for large companies to comply. They claimed

that these costs would not be offset by any substantial gain in safety . . ." [26].

14. Summary

1. Ground fault circuit interrupters are designed to open electric circuits prior to the time a normal adult or child would receive energy sufficient for electrocution; a person would, however, ordinarily feel the shock.

2. There is increasing use of GFCIs in this country

because of increasing requirements in Codes and other

rules issued by enforcing authorities.

3. There was wide use of GFCIs in some foreign

countries prior to their extensive use in the USA.

4. The effectiveness of GFCIs has been demonstrated by tests on dogs. (See section 11.3).

5. Principal controversies concerning GFCIs involve

nuisance tripping, reliability over an extended period

of time and the application of GFCIs to older buildings.

6. Because of leakage currents encountered in wire

and other electrical equipment in various locations and applications, there are controversies concerning

the feasibility of GFCIs.

7. A principal detriment to the feasibility of GFCIs

appears to be the questionable reliability because of

the frequent routine testing (monthly operation of the

test button) which is required; such testing appears

impractical to enforce in residential occupancies.

8. The rationale of requiring permanently installed GFCIs in new buildings, but largely ignoring older buildings needs to be examined.

9. The practical problems of leakage current ap- pears to be the principal technical parameter which

needs investigation for the use of GFCIs in older

buildings.

15. Recommendations

1. Additional laboratory and field investigations

involving nuisance tripping and reliability aspects of GFCIs should be performed.

2. The feasibility and need of GFCIs in various applications and in various locations needs investigation.

The need for GFCI protection of branch circuit wiring

should be evaluated by the Occupational Safety and

Health Administration or the Consumer Product

Safety Commission.

3. Leakage current data, particularly on wiring and

other electrical equipment in older buildings, should

be obtained.

4. The rationale of requiring the use of GFCIs in older buildings and appropriate methods to implement such requirements should be undertaken by an

appropriate group such as that indicated in Recommendation 2 above.

5. Standards for GFCIs to be used on older in- stallations should be developed after appropriate

leakage current data has been obtained.

6. Work concerning the adaptation of GFCIs for use on circuits with flat conductor cable should be

initiated.

7. Additional data on shock hazards particularly as

it pertains to children, the elderly and infirm should

be obtained as background information for GFCI

technology.

12
16. References

[1] Ground Fault Circuit Interrupters, Underwriters' Laboratories Standard 943 December 11, 1972.

[2] National Electrical Code, 1975 Edition, ANSI Cl-1975,

NFPA #70-1975, published by National Fire Protection Association

[3] Hankins, James D., and Garden, James R., Surface mounted flat conductor cable for hom(; wiring. Electrical Development Branch Research Division, Process Engineering Laboratories, Geo. C. Marshall Space Flight Center, October 1972.

[4] Dalziel, Charles F., Electric shock hazard, IEEE Spec- trum, 9, No. 2, 41-50, (Feb. 1972)

.

[5] Dalziel, Charles F., and See, W. R., Reevaluation of lethal electric currents, IEEE Transactions on Industry and General Applications, IGA—4, No. 5, 467-476

(Sept./Oct. 1968).

[6] Dalziel, Charles F., Transistorized ground-fault interrupter reduces shock hazard. IEEE Spectrum, 7 No. 1, 55-62,

(Jan. 1970).

[7] Kouwenhouen, W.B., Knickerbocker, G.G., Chestnut, R.W., Milnor, W.R., and Sass, D.J., A-C shocks varying

parameters affecting the heart, AIEE Trans. (Communication and Electronics), 78, 163-169, (May 1955).

[8] National Electrical Safety Code, Part 1, Rules for the

Installation and Maintenance of Electrical Supply

Stations, ANSI C2-1971.

[9] Olive, William W. Jr. The differential transformer and

its role in electrical safety. Record of the IEEE 1968 Region 3 Convention

[10] Position paper on grounding of appliances and electrical systems PB 194 185, Prepared under the auspices of the National Commission on Product Safety for the Information of the Commissioners, by the Ad-hoc Task

Force on Grounding, Myron Domsitz, Chairman, Re- produced by National Technical Information Service, June 16, 1969

[11] National Commission on Products Safety, Final Report

Presented to the President and Congress, June 1970, pages 26-28

[12] Smoot, Arnold W. Lethal electric shock, Lab Data, UL Autumn, 1970.

[131 Glowing electrical connections, results to be published

by W. J. Meese and R. W. Beausoliel, National Bureau of .Standards

[141 National Electrical Code, 1968 Edition ANSI CI 1968, NFPA #70-1968, published by National Fire Protection Association.

[151 National Electrical Code, 1971 Edition ANSI C1-197I,

NFPA #70-1971, published by National Fire Protection Association

[16] Code of Federal Regulations Lai)or 29, Part 1900 to end,

revised as of July 1, 1974, puijiished by the Office of the Federal Register, National Archives and Records

Service, General Services Administration Paragraph

1910.304, National Electrical Code, page .581. [17] Murphy, C.E., Electrical safety-ground fault interrupters. Oak Ridge National Laboratory, Internal Report TN4299, (Aug. 1973)

[18] Ground Fault Sensing and Relaying Equipment, Underwriters Laboratories Standard 1053, 1972. [19] Electrical Construction Materials List, Underwriters

Laboratories, June 1974, pages 100-101.

[20] Dutton, James E., Ground fault protection for people. Conference Record of the Eighth Annual Meeting of IEEE Industry Applications Society, October 8-11, 1973, Milwaukee, Wisconsin.

[21] Misencik, John J., and Mason, G.B., Ground Fault Circuit Breaker Optimizes Protection of People and Equip- ment, Westinghouse Engineer, 33, No. 3, 83-85, (May

1973).

[22] National Electrical Code, 1965 Edition, ANSI Cl-1965,

NFPA #70-1965, published by National Fire Protection Association

[23] American National Standard for Leakage Current for Appliances, ANSI ClOl.l—1973. [24] Underwriters' Laboratories, Fact-Finding Report on Ground Fault Circuit Interrupters, File E45269, March

1, 1972, Sponsored by National Electrical Manufactures Association, New York, New York.

[25] Preprint of the Proposed Amendments for the 1974

National Electrical Code, Part II NFPA No. 70P 4 74B.

[26] Federal Register, 40, No. 67—Monday, April 7, 1975, De- partment of Labor, Occupational Safety and Health

Administration [29 CFR Parts 1910, 1926], Docket

No. S-102, pages 15,390-15,392.

13
I tJBS-114A (REV. 7-73)

U.S'. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1 PTIRT IPATTON OR R F POR T NO

NBS BSS- 81

2a Gov t Accession

No.

3« Recipient s Accession No.

A. TITLE AND SUBTITLh

SURVEY OF GROUND FAULT CIRCUIT INTERRUPTER USAGE FOR

PROTECTION AGAINST HAZARDOUS SHOCK

5. Publication Date March 1976

6» Performing Or^sniz^tion Code

7. AUTHOR{S)

Robert W. Beausol iel and William J. Meese

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 462 A 193,

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

SAME AS ITEM 9

13. Type of Report & Period CoveredFinal

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Crad Number: 76-608069

16. ABSTRACT (A 200-word or less factual summary ol most significant information. If document includes a significant

bibliography or literature survey, mention it here.).

The ground fault circuit interrupter (GFC I ) is increasingly becoming an integral

part of building electrical systems to protect human life. Building researchers,

designers, and contractors should have a working knowledge of their purpose and

operational characteristics. This report describes the functional principles of

GFCIs and relates their performance to effects of electric current on the human

body. Information concerning the history, research and testing, installation

practices, fire protection aspects, types, manufacturers and costs of GFCIs are

included. The trend of requiring installation of GFCIs on more and more electrical circuits by regulatory authorities for safety purposes is outlined. Controversies concerning feasibility, reliability, nuisance tripping and other problems

are discussed; laboratory and field investigations addressing these problems

should be undertaken.

Permanent Installations of GFCIs are being made in new residential and other

construction, but very few are being installed In older buildings. The rationale

for this needs to be examined. Because of higher leakage currents probable in

most older construction, GFCIs manufactured under present standards may not be

feasible in older buildings.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Branch Circuit Protection, Electric Shock. Electrical Safety, Ground Fault, Leakage

Current, Prevention of Electrocution.

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